This background and documents mentioned below are provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention, and in particular allowing the reader to understand advantages of the invention over devices and methods known to the inventor, but not necessarily public. No admission is necessarily intended, nor should be construed as admitting, that any of the following documents or methods known to the inventor constitute legally citable and relevant prior an against the present invention.
Concrete foundations for telecommunications towers such as cell phone towers as well as wind turbine towers are now frequently employed. Such concrete foundations, particularly in terrestrial applications (as opposed to “at sea” applications) serve to support and prevent such tower structures from toppling, and generally avoid the need for additional supporting guy wires radially extending outwardly from the lower, thus avoiding the resultant large spatial area that such guy wires surrounding the tower otherwise consume.
U.S. Pat. No. 9,096,985 entitled “Foundation with Stab, Pedestal, and Ribs for Columns and Towers” teaches a foundation with a number of components, namely a central vertical pedestal, a horizontal bottom support slab, and plurality of radial reinforcing ribs extending radially outwardly from the pedestal, and a three-dimensional network of vertical, horizontal, diagonal, radial and circumferential post-tensioning elements embedded in the footing (support slab) which reduce stress amplitude and deflections. Disadvantageously, while such configuration allegedly allows pre-casting of some components to thereby reduce the amount of concrete cast in situ, some in situ casting of concrete is still required (ref. col. 3, line 65-col. 4, line 12). In situ casting presents a problem in harsh weather conditions, where proper curing of cast concrete structures may be inhibited or prevented.
US 2014/0215941 entitled “Tower Foundation” teaches a tower foundation comprised of a base slab, cruciate (cruciform) pillar slabs (two shown) stacked on each other and on such base slab, and a crown slab “capping” such structure. All slabs are of precast concrete. Steel guide rods are provided that have externally threaded ends to hold the individual elements components together and exert a compressive stress when tightened. Disadvantageously, however, the base slab disclosed in US 2014/0215941, as further referenced in U.S. Pat. No. 5,257,489 incorporated therein by reference, is of a solid (non-modular) configuration. For large towers such as large wind turbines towers where the wind turbine generates upwards of 7 MW and the resulting weight and wind forces acting thereon are substantial, the base slab is required to be large. In such circumstances a foundation design providing for modular construction of the base dictates that the pre-cast integral base member is of such a size that transportation thereof via truck to an installation site becomes difficult and expensive, if not impossible. Moreover, cell phone and wind turbine towers typically being cylindrical cannot therefore be directly coupled to cruciate pillar slabs, and such design thus further requires the circular crown slab mounted on such cruciate slabs to allow coupling to a circular base of a the tower to the foundation. Disadvantageously, however, in the foundation design of US 2014/0215841, circular crown slab 13 is thus unsupported in regions in which it does not overlie the cruciate pillar slabs. Additional thickness and reinforcement (and thus additional weight) is thus required to allow the crown slab to withstand bending forces which are exerted thereon at all locations about its periphery by the wind turbine tower to which it is coupled. Such additional weight of the crown slab negatively exerts additional compressive forces on the cruciate members and thus also the base member, requiring them in turn to be of thicker construction and thus adding still further greater expense to the foundation of such design.
US 2014/0033628 (now U.S. Pat. No. 9,175,670) entitled “Precast Concrete Post Tensioned Segmented Wind Turbine Tower” teaches a tower of stacked vertical cylinders, held together by post-tensioning of external and/or internal tendons (cables). The stacked cylinders rest on a concrete foundation 30, which foundation is not disclosed as being modular. Use of such cables 38, where disclosed as being used internally, due to their flexible nature, make it difficult to place such cables in apertures in the pre-cast stacked cylinders, due to the inability to “push” on such flexible cables so as to insert them in pre-cast apertures in the cylinders. Moreover, due to the need to anchor such (internal) cables at one end in the base 30, and as cables are not amendable to being secured into helical inserts, the base must be designed to allow access to cable ends exiting the base, as shown in FIG. 20, to allow such cable ends to be anchored. Such typically, as shown in FIG. 20, requires curved cable runs within base 30. Curved cable runs are definitively inferior to direct linear path lines, as such direct linear paths allow application of 100% compressive loading to members to offset any tensile loads (concrete having high compressive strength but poor tensile strength). Practically, therefore, tower members of this construction, due to use of flexible cables, may have increased complexity in construction and thus time to construct such foundation, to say nothing of decreased strength and resistance of components such as the base member to withstand loads applied thereto due to lateral and multi-axial forces applied to the tower due to arcuate cable runs therein.